“We Are in a War Zone Against this Disease.”
Climate change is fueling fire blight, and northern Michigan’s apple orchards are at risk.
By Todd VanSickle | Oct. 5, 2019
What is this contagion? What does it mean for the future of our fruit and orchards? And what — if anything — can we do about it?
In southwest Lower Michigan in 2000, fire blight ripped through a large portion of the region’s apple orchards. The hot, moist spring weather helped the contagion-causing bacteria spread and resulted in the death of 400,000 fruit trees. In the end, the epidemic resulted in $42 million of losses, crippling that region’s apple industry.
While Up North apple farmers empathized with their Lower Michigan counterparts, they were — back then at least — fairly safe from fire blight; our cold winters and springs traditionally kept the bacteria that causes fire blight,Erwinia amylovora,at bay.
Climate change is changing that.
Dr. Nikki Rothwell, Northwest Michigan Horticultural Research Center coordinator and district horticulturist works with about 500 farmers from around northern Michigan. She said the bacteria is a real — and increasing — concern.
Over the years, fire blight has been scarce in northern Michigan due to the cooler weather, which has helped keep the bacteria at bay. But warmer, wetter temperatures — exactly what we saw during the heavy rains of late spring and early summer 2019 is making fire blight more prevalent in the region.
“These bacteria can crank up to huge numbers in a relative short amount of time,” Dr. Rothwell said. “It is driven by temperature. The higher the temperature, the quicker the bacteria can reproduce.”
“Now that the climate is changing, and things warm up often earlier, it’s like a petri dish. We are seeing fire blight more often than we have in the past,” she added. “… Michigan has always had issues with fire blight, but northern Michigan really hasn’t had to worry about it.”
FIRE BLIGHT: SCIENCE & HISTORY
There are two different types of fire blight: blossom and shoot. In both cases, the infected tree begins to turn brown, limb by limb, shriveling any fruit in its path and eventually killing the entire plant.
Shoot blight occurs primarily in trauma events, such as hailstorms that rip up tree leaves, allowing the bacteria to enter through the damaged area of the plant.
To make things worse, researchers and growers have seen a new type of shoot blight this season. The new version occurs when shoots grow so fast that the tender tissues of the tree are left vulnerable to the bacteria.
Blossom blight affects trees in the spring when the flowers bloom and the bacteria colonize in the flower. The rain or heavy dew then washes the bacteria into the plant.
Although it’s been gaining traction in northwest Lower Michigan Fire blight has been in America longer than apple trees themselves.
Unlike Dutch elm disease or chestnut blight, which both came from somewhere else, fire blight is thought to have evolved on native trees in the Rosaceae family in North America long before apple trees arrived with European settlers in the 1600s. The fruit trees, which evolved in central Asia, had no defense against the native-born fire blight. Once in America, however, the trees became infected by the disease, which gave them the appearance that they were on fire.
“It is an invasive in reverse,” said Dr. George Sundin, a professor and tree fruit pathologist with Michigan State University. “In this case, we brought a new host, and the pathogen was here, and it jumped on the apples and pears. It was worse on those trees than the native species.”
IN THE LAB
For the past 10 years, Dr. Sundin has been ramping up his fire blight research. He has made breakthroughs with a plant growth regulator, which prevents the plant from growing excessively — something that could combat the newest version of shoot blight. The method mimics a hormone that not only controls the growth but also thickens the plant’s cell walls, making it more resistant to the bacteria.
“We are in the war zone against this disease,” Dr. Sundin said. “It is not necessarily trial and error — it is things we know are effective, but they need to be more effective. If the disease takes off, it can spread so quickly.”
Some other approaches include spraying a copper treatment on the tree, which has been effective but makes the apples russet in color — not ideal for the market.
“Russet doesn’t hurt anything, but consumers are used to perfect fruit,” Dr. Rothwell said.
Researchers are also exploring ways to deploy phages — naturally occurring viruses — to prey on the bacteria.
“We have been looking at what kind of different phages are out there,” Dr. Rothwell said. “These are naturally out there, and they are naturally going to kill the fire blight bacteria.”
Right now, growers typically combat blossom blight by applying an antibiotic to the tree to fight the infection, but time might be running out on that remedy; the bacteria is becoming resistant to some antibiotics, like Streptomycin.
There has been some success with other antibiotics but spraying also can be ineffective if it rains too soon after application and is washed off the plant.
Note to worried consumers: The antibiotics are used on a limited basis and sprayed on during bloom, which is three to four months before harvest; any remnants of the application is gone by time the apples reach market.
“There is no antibiotic residue on the fruit when it is harvested,” Dr. Sundin said. “It doesn’t impact what the consumer eats.”
MONITORING BY THE HOUR
Growers use an online weather map hosted by Michigan State University at enviroweather.msu.edu that gives Epiphytic Infection Potential models on an hourly basis and measure the potential of how fast bacteria can grow. The weather stations that collect the data are located in farms throughout the state.
“Consumers should know that growers aren’t just spraying for the heck of it,” Dr. Rothwell said. “They are spraying according to a model that is driven by research.”
Fire blight isn’t new for farmer Travis Bratschi, who owns and operates Bratschi Orchards on Elk Lake Road between Williamsburg and Elk Rapids. But there is more of it this year.
“It seems like every year we get a little bit of it,” Bratschi said. “Some years are worse than others. This year we have had it more extreme than what we have had it in the past.”
Bratschi follows the MSU online weather model to determine when to spray.
“We very much rely on that,” the grower said. “We spray when the model tells us to. That is really our option to combat it.”
The farmer uses a couple of different spraying applications including an antibiotic and a preventive chemistry that helps turn the plant’s defensive mechanisms on.
Bratschi said this year’s wet conditions left most farmers spraying twice as much as they normally do. During a typical drier season, he estimates that he would spray about three times in a season.
“Fire blight is among one of the biggest concerns from a spray perspective,” Bratschi said. “You have to be diligent. … It is better to be proactive than reactive.”
COST AND LOSS
Depending on the spraying application, the cost ranges between $25 and $50 per acre per each spray.
“I wouldn’t necessarily say we are pushing those costs into the final product, because we aren’t setting the final product price, but from a grower’s perspective it is decreasing our return because we have to spray more,” Bratschi said.
According to the American Phytopathological Society, fire blight cost United States farmers $100 million in losses each year.
Bratschi’s crops were infected more by shoot blight than the blossom blight, he said.
“We are use to it coming in on a bloom,” Bratschi said. “It came in on that tender vegetative growth. I think we controlled it though.”
He estimates that about 200 to 300 of his trees have been damaged by fire blight. Ultimately, Bratschi pulls the trees out of the ground and burns them.
“In an older tree, there are some theories that you can prune it back, but with a younger tree it isn’t even worth battling it,” Bratschi said.
A lot of Bratschi’s trees come from Washington state. It cost about $10 per tree to replant, but there are other costs, including the time and labor associated with replacing the tree.
Bratschi’s crops primarily consists of honey crisps and galas. All told, he has about 25 acres of apple trees. He said that fire blight is more consistent in the galas, than the honey crisps. However, he doesn’t have any intentions of eliminating galas from his orchards, but he will consider a different approach when setting up his next orchard.
Bratschi started farming in 2011 when he planted blocks of apples in alternating rows by variety — four rows of apple crisp, two rows of gala and so on. Moving forward he plans to have larger blocks of one variety, like eight to 10 rows of the same apple. He believes this could help contain the fire blight more effectively.
Fire blight also comes in the form of cankers on the trees that ooze and attract bugs that then spread it to other trees. The closer the trees are to each other, the faster the bacteria spreads.
“Each one of those ooze droplets have millions and millions of bacteria,” Dr. Rothwell said.
Bratschi, like many other growers in the area, use high-density trellis systems. The fruit trees are very close together and produce high quality apples at a high yielding rate. From an economic standpoint, growers prefer this system because the return on their investment is very good. However, the close proximity of the trees in the high-density trellis system comes at a high risk; it’s also very conducive to spreading fire blight.
“The return on investment is not good if you get fire blight,” Dr. Rothwell said. “Those high-density systems make you money faster, and they pay you back faster, but the problem is the fire blight issue, which has the potential to cause an epidemic.”
WHAT’S NEXT UP NORTH
Knowing how many trees have fallen victim to fire blight in northern Michigan is difficult to quantify.
“We don’t really have good numbers in Michigan. It’s hard to do when a grower is amidst a situation where they are losing all these trees,” Dr. Sudin said. “It is kind of hard to say, ‘I would like to go and count all your dead trees.’ It is such an emotional thing for a grower, because it is their livelihood. We are mostly working with them to save the rest of their trees.”
Locating hot spots is a little easier. Dr. Rothwell said the area east of Traverse City has been hit the hardest.
Despite challenges with controlling fire blight, researchers remain optimistic in their fight against the bacteria.
Rothwell said she doesn’t believe the region will see anything like the southwestern Michigan epidemic in 2000 but admitted there might be years where five to 10 percent of the trees Up North might have to be removed due to fire blight.
“I think we are going to be able to manage this,” Dr. Rothwell said. “I don’t think this is going to be to the point where we aren’t planting apples in northern Michigan any more. … Technology will solve some of our issues, but I think fire blight is just something we will have to deal with.
“Some years will be worse than others,” she added, “but climate is not on our side.”
Michigan is the nation’s third largest producer of apples. There are more than 11.3 million apple trees covering 35,500 acres on 825 family run farms in Michigan, according to the Michigan Apple Committee.